The present invention is directed to a bearing retainer and, more particularly, to a bearing retainer for maintaining constant intervals between the rolling elements that support the spindle of a bicycle or the like.
A retainer (cage) is a component for maintaining constant intervals between the rolling elements of a rolling bearing. Ball retainers are used with ball bearings, and roller bearing retainers are used with roller bearings. Depending on their manufacturing methods, there are pressed cages, which are obtained by the pressing of thin sheets (sheet metal); machined cages (hereinafter referred to as "retainers"), which are obtained by the cutting of ring-shaped blanks; and the like.
When preassembled bearings for supporting rotating or fixed spindles are assembled to the spindles, it is sometimes impossible to fit a metal retainer on an end portion of a spindle when the outside diameter of the spindle exceeds the inside diameter of the retainer. A retainer made of a synthetic resin can be stretched somewhat within its limits of elasticity, so the inside diameter of the retainer can be increased slightly. However, changes are not permitted in excess of the modulus of elasticity of the resin without damaging the retainer. Thus, in some cases it becomes impossible to assemble bearing components. A method for cutting annular retainers to allow increased radial expansion has been known in the past (e.g., Japanese Laid-Open Utility Model Application 56-91923). However, such cutting tends to deform the retainers and makes it impossible to stably retain the rolling elements.
A bicycle is equipped with crank spindles, hub spindles, and other spindles. The two ends of a crank spindle may be equipped with a rectangular cross section in order to fix the cranks. These types of crank spindle are referred to as a cotterless type. Ideally, these spindles should have minimum weight because motive power is provided by human effort. A known technique of weight reduction is to use hollow crank spindles in place of solid ones (e.g, Japanese Laid-Open Utility Model Application 52-60058). However, in a crank spindle, constant torsional stress and other loads are applied because the crank receives the tread force of the left pedal, captures this force as a torsional torque, and transmits this torque as motive power to the chain via the front chainwheel. When a hollow crank spindle is adopted, increasing the inside diameter of the hollow portion reduces the wall thickness of the corresponding part of the spindle. This, in turn, reduces the strength of the spindle. In order to provide sufficient weight reduction while maintaining strength, it is desirable to increase the outer diameter of the spindle. In addition, the inner bore of a hollow crank spindle should be maximized because of the limitations imposed by boring tools.
The Applicant has already proposed a structure in which the crank spindle and the left and right cranks are joined by serrations formed on the outer peripheral surface of the crank spindle in order to enhance the strength of the joints. This structure is disclosed in Japanese Patent Application 8-46657. The bonding strength of the crank attachments of the hollow crank spindle can be enhanced by increasing the diameter of these attachments.
Unfortunately, the bore diameters of the bottom brackets for supporting crank spindles are standardized. Also, because a crank spindle is supported by rolling elements in the inner bore of the bottom bracket, gaps are needed for the rolling elements and for the fixed cup and the adjusting cup that support the rolling elements. Thus, the diameter of the middle portion of the hollow crank spindles supported in the bottom bracket cannot be increased arbitrarily.
One possible solution to the limit placed on the diameter of the middle portion of the spindle is to increase the diameter of the ends of the spindle while maintaining the diameter of the middle portion of the spindle sufficiently small to fit within the bottom bracket shell and accommodate the bearings. However, since the bearing retainer used to mount the bearings to the middle portion of the spindle must have a diameter equivalent to the diameter of the middle portion, the bearing retainer cannot be moved past the larger diameter ends of the spindle, thus making it impossible to assemble the bearings. As a result, it is sometimes impossible to obtain effective weight reduction while maintaining the required strength of the spindle.